This invention relates to a method and apparatus for treating paper with other material in repetitive patterns. More particularly, the invention relates to a method and apparatus whereby repetitive treatment patterns are created by a displacement transfer apparatus.
Methods for altering or enhancing the characteristics of paper are well known in the papermaking art. For example, many techniques have been developed for imprinting or coating paper webs. These include gravure presses, blade coating, roller coating, silkscreening and stenciling methods. Bogardy U.S. Pat. No. 4,968,534 describes a stenciling apparatus wherein a continuous stencil comes into facing engagement with a paper web during the application procedure. The apparatus includes a preparation step where air is evacuated from the web through the pattern stencil prior to the application step in order to facilitate the treatment procedure. The pattern applied by the device can be altered by changing the stencil used.
The apparatus of Bogardy U.S. Pat. No. 4,968,534 is typical of many of the other previously known treatment devices because the apparatus contacts the paper web during the application process. These previously known devices, as a result, can only be used at points in the papermaking process where the paper is sufficiently stable to withstand the contact. This limits flexibility in placement of these devices, because the devices cannot be incorporated in a papermaking machine at relatively early stages of the papermaking process.
Stenciling and other previously known methods generally transfer a predetermined pattern to a treated article. The only way to change the pattern applied is to replace the pattern-forming element of the device. In other words, there is no easy way to alter the pattern by, for instance, merely changing operating parameters. This characteristic particularly limits the applicability of these devices in mass-production situations where it is desirable to apply several patterns to paper being produced.
A particular limitation of devices like that of Bogardy U.S. Pat. No. 4,968,534 is that a stenciling device incorporating a pattern for applying relatively-closely spaced bands of narrow width to cigarette paper would experience flexure of the stencil and resultant pattern non-uniformity when scaled to the size of a papermaking machine of the type used to make the paper.
Improved methods for altering the characteristics of paper which overcome these limitations are of particular interest to cigarette manufacturers. Cigarette manufacturers have long appreciated the usefulness of adding flavorings or burn control additives to paper. More recently, it has been recognized that cigarette paper could be altered so that smoking articles incorporating the altered paper will have a reduced burn rate when the smoking article is not drawn on by a smoker.
Paper cigarette wrappers have burn characteristics, including burn rates and static burn capabilities. It is known that burn characteristics can be modified by adding fillers, coatings, or other additives to papers. Copending, commonly-assigned U.S. patent application Ser. No. 07/614,620, filed Nov. 16, 1990, which is hereby incorporated by reference in its entirety, includes a description of many of these methods, and also discloses a nonlaminated paper of variable basis weight and suggests that burn rate control of that paper can be achieved economically with mass-production techniques. The variable basis weight is achieved by applying bands of cellulosic slurry in a pattern to a moving paper web during production while leaving regions of the paper between the pattern untreated. The basis weight of the paper is increased in regions where the slurry has been applied, and when the paper is incorporated in a smoking article, the smoking article has a decreased burn rate in those regions. Limitations of previously known mass-production application methods like that disclosed in Bogardy U.S. Pat. No. 4,968,534 render them less effective for altering the basis weight of cigarette paper in patterns as described in above-incorporated U.S. patent application Ser. No. 07/614,620.
It would be desirable to provide a durable apparatus which can be inexpensively manufactured and easily incorporated into a papermaking machine at various points in the papermaking process.
It would be desirable to provide a method for treating a paper web where the pattern applied to the web can be changed by altering machine operating parameters.
It would be desirable to provide an application method in which a large quantity of web is treated with material in uniform patterns, in a continuous manner, and at high speeds.
It would be desirable to provide an application method where the amount of material applied can be accurately metered.
It would be desirable to provide an application method and apparatus for applying chemical treatments to cigarette paper so that burn rate control can be achieved economically with mass production techniques.